Abstract

Background: Many adults with autism spectrum disorder (ASD) go undiagnosed. Specialist adult assessment services play a key role in the detection of these cases. However, such services are often overstretched. It is proposed that the Autism-Spectrum Quotient (AQ), a self-report questionnaire measuring autistic traits, could reduce unnecessary referrals if those scoring above a cut-off on the AQ were prioritized for assessment. However, the ability of the AQ to predict who will receive a diagnosis of ASD is unclear.

Method: We studied a consecutive series of 476 adults seen by a national ASD diagnostic referral service on suspicion of ASD. We examined whether AQ scores predicted ASD diagnoses made by clinicians using ICD-10 criteria and informed by the Autism Diagnostic Observation Schedule Generic (ADOS-G) and Autism Diagnostic Interview Revised (ADI-R).

Results: Scores on the self-report AQ did not predict expert clinical diagnosis any better than chance. The AQ showed high sensitivity of 0.77 (95% CI: 0.72-0.82) but low specificity 0.29 (0.20-0.38), and while the Positive Predictive Value (PPV) was high 0.76 (0.70-0.80), the low Negative Predictive Value NPV of 0.36 (0.22-0.40) indicates that nearly two thirds of those who scored below the cut-off were 'false negatives', screening negative but receiving a diagnosis of ASD. A comorbidity analysis revealed that generalized anxiety disorder (GAD) may 'mimic' ASD and inflate AQ scores, leading to false positives.

Conclusions: The AQ has limited utility for screening referrals. Recommendations (e.g. UK guidelines) supporting its role in the assessment of adult ASD may need to be revised.